Currently, automatic teller machines for cash notes have been of wide use and cash note counting and sorting machines for counting and sorting cash notes have also been widely applied, both of which are provided with a plurality types of magnetic sensors with high sensitivity to detect anti-counterfeiting information of bank notes. Since magnetic anti-counterfeiting information in a cash note is very weak, a fine amplifying circuit with low noise and extremely high magnification is needed to detect the magnetic information. The inherent characteristic of the amplifying circuit with high sensitivity is that it is susceptible to interference, and in practical application, the automatic teller machine is not always easy to move due to restrictions on operational environment and installation method. When a high-power transformer or alternating-current electrical equipment exists near the automatic teller machine, with a large increase in electrical load, the intensity of a power-frequency electromagnetic field generated through space radiation increases rapidly and an interference source beyond the normal tolerability of the equipment may be generated quite easily. Even though the electrical equipment has passed various kinds of electromagnetic compatibility certification, power-frequency interference signals may be induced in the high-sensitivity magnetic sensor, which include low-frequency interference signals of 50 hertz and 60 hertz or higher-harmonic interference signals of several hundred hertz, and the interference signals will be outputted with their level superimposed on that of the effective anti-counterfeiting signals detected by the sensor.
In the operating process of an existing automatic teller machine for cash notes and an existing cash note counting and sorting machine, anti-counterfeiting information collecting is performed on deposited cash notes and withdrawn cash notes synchronously. The cash notes pass through an induction region in sequence at a certain interval. The sensor collects and obtains magnetic anti-counterfeiting information from each cash note passing by it, and determine whether the anti-counterfeiting information is correct by computation processing or data comparison to identify authenticity of the cash note.
During the process of the sensor collecting and obtaining magnetic anti-counterfeiting information from each cash note passing by it, if the effective anti-counterfeiting signal collected by the sensor is interfered, incorrect anti-counterfeiting signal voltage waveform may be collected by the sensor and thus misjudgment may be made by an equipment. As a result, the equipment is incapable of identifying anti-counterfeiting information of the cash note normally, and deposit rejection or withdrawal rejection occurs in large numbers. At this time, the financial equipment can not work properly due to special security requirements on financial equipment. Moreover, since there are plenty of magnetic sensors in an automatic teller machine (ATM) or a cash note counting and sorting machine and the sensors are installed in different locations in the equipment, interference signals detected from the sensors are of significant difference, referring to FIG. 1, which is a schematic diagram of difference between interference signals detected from two sensors at different locations in the equipment, thus the difficulty of elimination of interference signals is increased. In the prior art, power-frequency interference is eliminated by way of complicated software algorithm and FFT transform in most cases. However, processing output signals of the sensors separately consumes considerable system resources and also tends to cause attenuation of effective signals. Besides, the prior measure of shielding space electromagnetic field to resist low-frequency electromagnetic interference requires an increased cost on shielding material, and the financial equipment may not be shielded completely for its application requirement. The measure of resisting interference applied to electrical equipment requires extracting power-frequency signals from mains supply, and the power-frequency interference signals extracted may have phase difference with interference signals coupled in the magnetic sensor by space coupling, so phase compensation is required, resulting in a complicated circuit. Furthermore, there may also be difference in the frequency information of the interference source, which results in the impossibility of restoring real interference signal accurately.